A cataract is formed by opacification of the crystalline lens or its envelope—the lens capsule—of the eye. The cataract obstructs passage of light through the lens. A cataract can vary in degree from slight to complete opacity. Early in the development of an age-related cataract, the power of the lens may be increased, causing near-sightedness (myopia). Gradual yellowing and opacification of the lens may reduce the perception of blue colors as those wavelengths are absorbed and scattered within the crystalline lens. Cataract formation typically progresses slowly resulting in progressive vision loss. If left untreated, cataracts may cause blindness.
A common cataract treatment involves replacing the opaque crystalline lens with an artificial intraocular lens (IOL). Every year, an estimated 15 million cataract surgeries are performed worldwide. Traditionally, cataract surgery has been typically performed using a technique called phacoemulsification in which an ultrasonic tip with associated irrigation and aspiration ports is used to sculpt the relatively hard nucleus of the lens to facilitate removal through an opening made in the anterior lens capsule. Access to the lens nucleus can be provided by performing an anterior capsulotomy in which a small round hole is formed in the anterior side of the lens capsule using a surgical. Access to the lens nucleus can also be provided by performing a manual continuous curvilinear capsulorhexis (CCC) procedure. After removal of the lens nucleus, a synthetic foldable intraocular lens (IOL) can be inserted into the remaining lens capsule of the eye.
One of the most technically challenging and critical steps in the cataract extraction procedure is providing access to the lens nucleus for removal of the cataract by phacoemulsification. The desired outcome is to provide a smooth continuous circular opening through which phacoemulsification of the nucleus can be performed safely and easily, and also through which an intraocular lens may be easily inserted. Because of the criticality of this step, some surgeons prefer a surgical laser beam over manual tools like microkeratomes and forceps since the laser beam can be focused precisely on extremely small amounts of eye tissue, thereby enhancing the accuracy and reliability of the capsulotomy procedure.
Several commercial laser-assisted eye surgery systems are available to facilitate cataract removal and astigmatism correction. The CATALYS Precision Laser System from Abbott Medical Optics is indicated for anterior capsulotomy, phacofragmentation, and the creation of single plane and multi-plane arc cuts/incisions in the cornea to correct astigmatism. The CATALYS System uses a two-piece liquid-filled interface that docks with the patient's eye and provides a clear optical path for real-time video, OCT imaging, and laser treatment. Aspects of the CATALYS System are disclosed in U.S. Pat. Nos. 8,394,084, 8,500,724, 8,425,497, U.S. Patent Publication 2014/0163534, U.S. patent application Ser. No. 14/256,307, filed Apr. 18, 2014 (published as U.S. Patent Publication No. 2015/0018674 on Jan. 15, 2015), and U.S. patent application Ser. No. 14/255,430, filed Apr. 17, 2014 (published as U.S. Patent Publication No. 2014/0343541 on Nov. 20, 2014), the contents of all of which are incorporated herein by reference as if fully set forth. Other systems for laser cataract surgery are the LenSx Laser from Alcon Laboratories, Inc., the LENSAR Laser System from LENSAR, Inc., and the VICTUS Femtosecond Laser Platform from TECHNOLAS Perfect Vision GmbH a Bausch+Lomb Company.
One drawback with current systems is with the docking interfaces between the eye and the laser system. Most docking interfaces rely on suction to hold the interface to the eye, and sometimes to hold separate pieces of the interface together. If during a laser procedure the level of vacuum in any of these couplings diminishes, an adverse event may occur. In particular with liquid-filled interfaces, the liquid is used as a transmission medium for the laser, and a loss of vacuum may introduce air which has a different index of refraction than the liquid and would affect the laser optics. Although detecting a sudden and significant pressure differential signals an adverse condition, sometimes pressure fluctuations do not lead to failure. Stopping the laser in the middle of the surgery when it is not necessary is also undesirable. Furthermore, in some instances of a vacuum loss, the water displaced from the patient interface is aspirated by the vacuum system, decreasing the effectiveness with which the system detects a vacuum loss event. Accordingly, there is a need for sophisticated systems for detecting such loss of suction.